Chemicals commonly known as oxygen scavengers are routinely added to water streams to reduce oxygen concentrations to minute levels. For example, oxygen scavengers are routinely added to boiler feedwater streams to minimize corrosion and deposits within the boiler equipment. In the electrical power industry, oxygen scavengers are added to the boiler feedwater streams to reduce dissolved oxygen in boiler feedwater to very low concentrations, frequently to less than one part per billion ("ppb").
Although the most commonly used oxygen scavengers, such as hydrazine and carbohydrazide, are added to boiler feedwater at temperatures of about 120.degree. F., the rate of reaction between the oxygen scavengers and oxygen in the boiler feedwater does not become rapid until the boiler feedwater reaches temperatures of about 275.degree. F. Only at these elevated temperatures will the oxygen scavenger react rapidly with dissolved oxygen in the boiler feedwater to quickly reduce the oxygen concentration to acceptable levels.
In the electrical power industry, this is generally not a problem because, under normal operating conditions, the recycled condensate is heated as it passes through successive heat exchangers so that the temperature of the feedwater stream is substantially greater than 275.degree. F.
During start-up, however, the boiler feedwater is frequently at substantially ambient temperatures. To reduce dissolved oxygen in these boiler feedwater streams, massive amounts of oxygen scavenger must be used. Alternatively, dissolved oxygen can be removed by heating the boiler feedwater with steam in a mechanical deaerator. Both of these methods can be very expensive. Also, use of massive amounts of oxygen scavenger can produce undesired levels of break-down products and by-products within the boiler feedwater unless additional procedures are employed to promptly remove the excess oxygen scavenger.
Prior attempts to solve this problem have included the attempts to develop a suitable catalyst which would accelerate the reaction of oxygen with the oxygen scavenger at ambient temperatures. So far, however, no catalyst has been found which is inexpensive, easy to use and does not result in increased contamination of the feedwater stream.
Accordingly, there is a need for a method of deoxygenating water at substantially ambient temperatures which is relatively inexpensive and easy to use and which does not contribute unwanted contaminants to the water.